Original Posted By: Mark Roberts
or 613.5, and jigs too...HA! Tim, that was the best said response to date of any of my postreplies.... Especially the Lose Weight part (all the years when I wasas skinny as a noodle and made fun of fat folk is coming back to bitme in the belly... My legs are still so skinny I have considered suingthem for non-support...)All kidding aside, I really do appreciate your reply, as it was a goodsummary of the design thoughts, and was presented very nicely--- (Not"Why the H#ll do you want to do that? Just build it the way hedesigned it!!")To update all:I did just hang up from a delightful 20 minute call to Harry Riblett.We discussed the airfoil and the plane design, and while I appreciatethat he has not built and flown a Piet, he does understand the basicdesign and the flight dynamics of it. Before i pass along his thoughts(as of today 7/22/10), I want to explain (again) why I would even messaround with the design in the first place.I'm 6'4" and 250lbs. Even with a dramatic weight loss, I'd still likemy wife to go along if the temp in Central California goes above 90degrees (about 6 months outta the year...).So, since my wife actually LIKES the Piet design (a first for the onesI have shown her), I'd like the extra lift I will need to flycomfortably.I called Harry to ask (as Oscar suggested.... Thanks Oscar!) whichwould be better for me to use: the GA30-612 or the GA30-613.5. (Hekept correcting me when I simply said 'the 612 or the 613.5... "It'sthe GA30-613.5..."). He said the GA30-613.5 was the one I would wantto go with due to the higher lifting co-efficient of the airfoil.He said about 1 degree of incidence would be good, as I mentioned thatLowell had to hold 30-40 lbs of forward stick at cruise.I also know that a couple of extra feet on the wing tips would help,and that I'll need to account for that in tail area as well.But, as to the 2 airfoils that have been batted about in the forum, heseemed to think the GA30-613.5 would be a better choice if one wasconsidering an alternative to the original FC-10.Now, I know there are lots of opinions about this, so I am not tryingto start another war, but just passing along the discussion I had withhim about the differences with the 2 airfoils for an open cockpit,draggy high wing design.It's a 19 year update on the original letter that he wrote and hasbeen posted on this forum in the past. :o0To those going to Brodhead, I envy ya'll.MarkOn Thu, Jul 22, 2010 at 2:00 PM, Tim Willis wrote:>> Mark,>> Riblett is certainly the authority on his own airfoils and any response you getwill no doubt be illuminating. Please share.>> This board likely knows more about Pietenpols and their flying characteristicsthan Harry Riblett, though, and has at least some anecdotal comparisons specificto Piets. We may know some stories Riblett does not know, and he some ofwhich we are uninformed, in mating Ribletts to Piets.>> What's more, I think YOUR choice to a degree, though, relates to what engineand what applications you have or intend. Do you have a 60+hp A-65 or a 90+hpCorvair? Do you want to get off the ground and over 50' AGL in a hurry, or wantto cruise faster? How is this preference reflected... do you have a climb propor a cruise prop? Is your challenging app to fly 1000 miles to Brodhead withfull fuel but a light load, as quickly as a Piet can, or to take a heavy friendflying on a hot day?>> Both Riblett airfoils are reputed to give more lift, less drag than the BP airfoil.No one has put them up to a side-by-side test.*** (see below)> None of them-- Riblett or BP-- unlike the NACA 2412, for instance, have beenin wind tunnels.>> Likely comparisons:>> --The 613.5 should have both more lift and drag than the 612.> --The 612 should have more lift and less drag than BP's FC10.> --The 612 should be faster than the 613.5 and BP's FC10.> --All else equal, you should attain 50' AGL faster with the 613.5> --You might have the gentlest stall with the 613.5... this remains to be seen.>> Some may rightly disagree with each of these statements.>> You can change a lot of the flight dynamics witha ANY airfoil by building thePiet as light as possible, powering it up a bit, and/or by adding some wingspan.>> With a thicker section and chord on a 613.5, little changes in the angle of incidence(from the 2 degrees of the FC10) might tune the Riblett quite differentlyto achieve a different optimum. Who has worked on this? Kept a lab book?Both considered and accommodated differential pitching moments?>> ***Note: Lowell Frank has had different wings, featuring BP's FC 10 and NACA2412, on the same plane with the same engine. Then he changed to a more powerfulengine. He has the closest to comaparative data. Some of the Riblett 612 and613.5s are just coming on line now. (If memory serves, check with Roman Bukolt,for instance.)>> This is just grist for the mill... there are many other considerations. Adherenceto the original design, with its well known envelope, are two. But it isyour plane and your applications.>> In my case, starting afresh, as a fat boy in a warm climate, with an A-65, Iwould go with the Riblett 613.5 and add wingspan, as well. And go on a diet, too.>> Tim in central TX>> -----Original Message----->>From: Mark Roberts >>Sent: Jul 22, 2010 3:11 PM>>To: pietenpol-list(at)matronics.com>>Subject: Re: Pietenpol-List: Riblett 612 or 613.5, and jigs too...>>>>>>Good idea Oscar. I did in fact try to call him on the issue a couple>>of months ago, and left a message, but I wasn't sure if he was indeed>>still around, so I chickened out on calling again. I didn't think to>>call back this time, so i think I will give another shout out to him>>on this issue.>>>>Thanks for the suggestion.>>>>Mark>>>>On Thu, Jul 22, 2010 at 5:54 AM, Oscar Zuniga wrote:>>>>>>>>> Mark;>>>>>> Why not ask Harry Riblett about the 612 vs. 613.5?>>> I believe he's still around and talks freely with>>> homebuilders.>>>>>> Oscar Zuniga>>> Air Camper NX41CC>>> San Antonio, TX>>> mailto: taildrags(at)hotmail.com>>> website at
http://www.flysquirrel.net> >>> ______________________________________________________________>>> >-->>Mark Roberts>>California Laser Etch>>www.california-laser.com>>888-882-5015>>888-882-5016 fax>>>>>>-- Mark RobertsCalifornia Laser Etchwww.california-laser.com888-882-5015888-882-5016 fax________________________________________________________________________________Date: Thu, 22 Jul 2010 17:56:16 -0700Subject: Re: Pietenpol-List: Riblett 612 or 613.5, and jigs too...